Validation of the BIOPAC indirect calorimeter for determining resting energy expenditure in healthy free-living older people

The BIOPAC indirect calorimeter for measuring resting energy expenditure (REE) is less cumbersome than many other calorimeters. We tested the hypothesis that the BIOPAC calorimeter is as well suited for determining REE in older people as traditional calorimeters. In 50 healthy persons (24 men and 26 women; age range, 61-83 years), REE by BIOPAC was validated against Vmax Spectra indirect calorimeter as a criterion method. Resting energy expenditure by BIOPAC was recorded at 2 different time intervals to find optimal conditions for older persons. Also, REE by 7 published equations was validated. The Bland-Altman procedure was used to test agreement between methods. Multiple regression analysis was applied to develop a new equation for predicting REE from BIOPAC. The BIOPAC calorimeter and most empirical equations significantly overpredicted mean REE in both sexes. Mifflin's equation best-predicted mean REE. Limits of agreement were wide for BIOPAC and narrow for most empirical equations. The Lührmann and Müller equations had smallest limits of agreement in men (±950 kJ/24 h) and the Harris-Benedict and Müller equations in women (±672 kJ/24 h). A new equation was developed for the BIOPAC device improving both predictions of mean and individual REE (R² = 0.671, standard error of the estimate = 136 kJ/24 h). Using this equation, 72.9% of subjects were lying within 10% of measured REE, compared with only 12.5% when using the manufacturer's algorithm. In conclusion, the BIOPAC calorimeter is suitable for measuring REE in healthy older adults when the new prediction equation is applied. This calorimeter is not applicable to frail older persons.